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Subject: TWL: RE: RE: RE: Batteries
From: frank weismantel (fxw@XXX.XXX)
Date: Fri Dec 27 2002 - 12:46:54 EST
Hello All,
I am NOT trashing Mike Schooley here.
Mike states that the telecom industry moved to AGM batteries from flooded
cells due to their higher current capacities. This is not entirely correct.
In the early 1990's we started building cellular systems in earnest. The
first round of cell sites called for an unprecedented increase in the number
of building permits applied for. Prior to the cellular industry, most
communication facilities were not permitted. Once all the various municipal
agencies saw the 8 foot wide by 4 foot high racks of lead acid battery
plants they began demanding sophisticated (Rube Goldberg) venting systems
for battery gases or separate vented rooms for battery plants. We were
trying to drive the per site costs down, not up, so the industry moved
wholesale to gel cell batteries. Unfortunately, at first we simply replaced
lead acid batteries with gel cells and didn't do a thing with our old style
ferroresonant rectifiers. Big mistake. Lots of gel battery plants were
frequently equalized and ultimately destroyed. Eventually, we figured out
reading the documentation that came with the batteries might be a good
thing.
Today we rely on flooded lead acid cells for really enormous battery plants
(thousands of AH) and most sub 1000 AH plants rely almost exclusively on AGM
batteries and high frequency switcher type rectifiers. Our plants are set
up so the batteries mainly provide filtering of the rectifier output and
offer the cell site equipment very smooth DC power. We think of a battery as
a giant smoothing capacitor. Telecom battery plants are placed in parallel
across rectifier output. Thus the rectifiers actually power the site
equipment. The batteries only take the load when the rectifiers fail. On
boats, batteries directly feed a DC buss that feeds all shipboard systems,
are on the input side of inverters and are the main supply of operating
power for shipboard systems. Telecom systems are hoped to rarely even
partially discharge. Thus batteries perform very different jobs for telecom
sites than for marine systems. The real benefits to telecom operators of
AGM batteries are no monthly maintenance, reduced size, no equalization
requirement and no out gassing. As usual it all came down to capital and
operating cost reduction.
So, why did I write all this? Simple. Our marine battery systems must be
designed to survive hundreds of charging cycles and a pretty adverse
environment. Regardless of what battery type we choose, our single biggest
contribution to battery life appears to be properly sizing the amp hours of
the plant to address the expected load and appropriate discharge percentage.
Once that mission is accomplished, choosing the appropriate charger type and
applying an appropriate charging schedule or charger program seems to be the
next logical step. Finally, maintenance of the plant, including corrosion
control (not mentioned in this thread but critical), becomes the last piece
of the puzzle needed to insure long life. The problem with shipboard
battery plants is that you must do lots of things correctly to insure they
live a long life, regardless of which type you choose. Throw in a dozen
accidental 100% discharges and all your planning and maintenance work can go
for naught with replacement looming as the only alternative.
If I were going world cruising I'd probably choose wet cells just in case I
needed to add a replacement in some far away land. There would definitely
be an AGM with separate charging system up on the flybridge or somewhere
above the bilge for powering my ssb and other safety critical communications
gear. If I were coastal cruising and never left the US, Canada, Australia,
NZ or other developed country I'd surely go all AGM (please don't flame me
for terming New Zealand "developed". They're big boaters, OK?). We make
choices for our own reasons and, if we do our homework, stand a good chance
of being satisfied with the result regardless of which technology we choose
(Murphy notwithstanding).
Just my opinion, feel free to trash it...
Frank & Claudette Weismantel
Elverta, CA
Boatless for a little while longer
-----Original Message-----
From: trawler-world-list-admin@XXX.XXX
[mailto:trawler-world-list-admin@XXX.XXX]On Behalf Of Michael
Schooley
Sent: Friday, December 27, 2002 8:34 AM
To: '1trawler world'
Subject: TWL: RE: RE: Batteries
SNIP
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